Regenerative air preheater

ABSTRACT

A stationary mass regenerative air preheater has a bypass for the one of its heat-exchange gaseous media which is to be conducted by the rotating hoods placed in the central core of the regenerative mass. A control valve is provided in or at the end of the bypass to govern the bypass ratio and may be of a form positively to shutt-off access of the one of the media to the heat-exchange mass. Each hood is communicable with the bypass, which extends continuously between the end faces of the mass.

United States Patent Kirchhoff Nov. 18, 1975 REGENERATIVE AIR PREl-[EATER Primarv Examiner-Albert W. Davis Jr. 75 l t F 1 nven or g g iz Klrchhoff Olpe Attorney, Agent, or FirmElliot A. Lackenbach [73] Assignee: Apparatebau Rothemuhle Brandt &

Kritzler, Rothemuhle, Germany [57] ABSTRACT [22] Filed: Aug. 31, 1973 A stationary mass regenerative air preheater has a by- [21] App! 393432 pass for the one of its heat-exchange gaseous media v t which is to be conducted by the rotating hoods placed [30] Foreign Application Priority Data in the central core of the regenerative mass. A control Sept. 1, 1972 Germany 323 1720.1 valve is Provided in or at the end Of the yp t0 em the bypass ratio and may be of a form positively to 52 us. Cl 165/4; 165/7 naeeess of the one of the media to the heat- [Sl] Int. Cl. F28d 17/00 exchange Each hood is communicable with the 58 Field of Search 165/4, 7 bypass, which extends continuously between the end faces of the mass.

[56] References Cited 1 Claim, 4 Drawing Figures U.S. Patent Nov. 18, 1975 1.; REGENERATIVE AIR PREHEATER FIELD OF THIS INVENTION DESCRIPTION OF DRAWINGS AND OF PREFERRED EMBODIMENTS FIGS. 1 and 2 show in side section on the line BOA This invention relates to a regenerative air preheater 5 and in plan section on the line CD, respectively, the

with a stationary cylindrical regenerating chamber and a bypass for air and/or flue gas.

BACKGROUND OF THE INVENTION Air preheatersofithiskind with bypass'd ucts are re quiredmore particularly for. operating ship s boilers. During starting and at light loads the flue gas :andair bypasses are utilised for regulating the cold-end temperature inorder to prevent fluefgases dropping below the dewpoint and to avoid the heating surfaces becoming polluted.

v FIGS. 1 and 2 show-,in diagrammatic form aknown system of thebypasses (4 and 11,),for fluegasand air in such a regenerative air'pre heater with a vertically disposed cylindrical regenerating chamber. Two air ducts "(4) and two gas ducts (11) are preferably disposed in a symmetrical plan view configuration within the free corner spaces of the square girder frame (13) of the regeneration chamber (1). The bypass ducts (4 and 11) are mounted on the regenerator housing with which they form an integral structural unit.

This arrangement of four bypass ducts which are disposed directly on the external circumference of the regenerative chamber greatly obstructs the accessibility to the regenerator housing.

SUMMARY OF THE INVENTION It has been proposed in German Pat. No. 1156929 to pass gases through a part only of a central core of an axially divided regenerator mass. But here there was no true bypassing, since what flows through part of the central core through one of the axially divided parts of the mass was necessarily reunited with the main flow in the other of the axially divided parts of the mass, and there was no provision for control of the ratio of flows passing through the core and through the one part.

According to the invention a regenerator is constructed so as to reduce the number of external bypasses which were previously provided and if possible to avoid them altogether.

The invention is based on the fact that it can suffice to provide only one true bypass duct for a medium, either for flue gas or for air, in order to regulate the coldend temperature by means of suitably incorporated" regulating elements.

According to the present invention a true bypass duct is provided between axial portions of rotatable hoods at each axial end face of a stationary regenerative mass by a passage extending continuously from one face to the other thereby offering a bypass duct past all the regenerative mass, and a centrally disposed variable obturator for the passage, whereby the one of the media normally conducted by means of the hoods through the regenerative mass may be bypassed past it to a predetermined controllable and variable degree. Control of the obturator may be automatic. The obturator may act either just to variably obstruct the bypass passage or may complementarily obstruct the bypass passage or access of the medium to the mass through the hoods.

A suitable obturator may be incorporated within the cylindrical core or at one face of the regenerative mass.

-' In the prior art construction the flue gases for heating the regenerator l are supplied from above through a stationary heating gas'duct 2 and then flow through an exit duct 3. Gas bypasses 4 are connected parallel thereto.

Cold air to be heated flows in the opposite direction from an air inlet duct 5 through a firstrotary hood 6, stationary heat-exchange'elements of the mass 7 and second rotary hood 8 via an air discharge elbow 9 into the exit duct 10 for heated airrBypasses' 11 are provided for the air. I v

As may be seen by reference to FIG. 2, the bypass ducts 4"and 11 are external of the regenerative mass, being mounted within the free corner spaces in the diagonals of the square girder frame 13 on the regenerator housing and forming an integral structural unit therewith.

In the embodiment of the invention shown in FIG. 3 a rotatable hood 6' has a pair of diametrically opposed portions in the shape of sectors of rings for conducting one of the heat exchange media (flue gas or air) to one axial face of the heat exchange elements 7 of the regenerative mass in the stationary chamber 1. A hood8' takes flue gas or air from the other axial face of the mass.

The regenerative mass has, however, a hollow core 12 about a central shaft 15 for the hoods, and offers a exchange elements. For controlling whether flue gas or I air shall flow through the bypass (as indicated by broken arrows) or through the mass, or partially through both, a variable obturator 14 is provided at one end of the passage, centrally of the mass and of the hood 6'. It is formed of a plurality of flaps able to be driven to the limit position shown in full linesin FIG. 3 to shut off gas or air flow through the bypass, or to the limit position shown in dot-dash lines in which they seat against the hood and shut off flow from the mass, or to any position in between, whereby the ratio of gas flowing through the bypass to that flowing through the mass may be controlled.

Apart from the presence of these flaps the centre (axial) portions of each of the hoods 6', 8' is in communication with the hollow core 12.

The flaps 14 may in certain circumstances be automatically applied, for example by means of thermal expansion rods indicated at 20 which adjust the flaps relacontrol the ratio of gas or air passing through the bypass to that passing through the heat exchange elements 7. a variable obturator I6 is provided inside the core in the form of a choke formed by a valve plate rotatable about an axis normal to that of the shaft whereby variability to obstruct the bypass passage. Total shut-off valve means 19 may be provided in the gas or air inlet duct 5.

The obturator 16 may be operated through manual controls or automatically, as indicated above.

The dash-dot line shows an external bypass 20 for the medium not passing through the hoods. This second bypass permits both media to bypass that outer portion of the regenerating chamber which is filled with heatexchange elements, for example in the event of total blockage of the mass.

The advantages achieved by the invention compared to the form shown in FIGS. 1 and 2, are due more particularly to the fact that further external bypass ducts are not normally required because the cold-end temperature is regulated by means of shut-off or regulating elements in a central flue gas or air bypass duct.

This provides all round free accessibility to the regenerator housing and leads to a substantial saving of ex ternal ducting and construction costs which were hitherto necessary.

What I claim is:

1. In a regenerative air preheater with a stationary regenerative mass having two end faces, two hoods rotatable about an axis over each said end face respectively to communicate one of the heat-exchange media to and from the mass, and a bypass for at least one of the media the improvement comprising a hollow core of the mass at the axis of rotation of the hoods and extending continuously from end face to end face of the mass and forming a gas-passing bypass duct completely through the axial length of the mass, a central portion of each of the two hoods communicable with an end of the bypass duct, and variable obturator means operable to vary the relative amounts of flow to the said one of the media through the mass and through the bypass duct wherein said obturator means comprises movable flaps at one end of the duct and operable also positively to prevent flow through one of the mass and the bypass duct. 

1. In a regenerative air preheater with a stationary regenerative mass having two end faces, two hoods rotatable about an axis over each said end face respectively to communicate one of the heat-exchange media to and from the mass, and a bypass for at least one of the media the improvement comprising a hollow core of the mass at the axis of rotation of the hoods and extending continuously from end face to end face of the mass and forming a gas-passing bypass duct completely through the axial length of the mass, a central portion of each of the two hoods communicable with an end of the bypass duct, and variable obturator means operable to vary the relative amounts of flow to the said one of the media through the mass and through the bypass duct wherein said obturator means comprises movable flaps at one end of the duct and operable also positively to prevent flow through one of the mass and the bypass duct. 